Long-term potentiation (LTP) was examined in hippocampal slices from Syrian hamsters entrained to a LD 14:10 cycle. Population spike (PS) amplitudes from CA1 pyramidal cells were measured before (control) and after tetanizing the Schaffer/collateral commissural pathway. Slices from animals sacrificed during the day, between zeitgeber time (ZT) 0430 and 0530, were incubated, and then tetanized between ZT 1340 and 1930, where ZT=0 denotes lights on. Slices from animals sacrificed during the night, between ZT 1830 and 1930, were incubated, and tetanized between ZT 0030 and 0410. LTP, a sustained increase in PS amplitude following tetanus, was evoked in both groups. PS amplitude increased by 102.7+/-20.3% in animals sacrificed during the day and by 48.0+/-7.5% in animals sacrificed during the night (p<0.05). Thus hamster slices prepared during the day show more robust LTP (a doubling of PS amplitude), a difference persisting in slices incubated for several hours.
Copyright 1999 Elsevier Science B.V.